This invention relates to the field of semiconductor manufacturing, and more particularly, to the field of etching dielectrics.
Types of dielectrics used in semiconductor manufacturing include oxides, nitrides, borophosphosilicate glasses (BPSG), silicon-dioxides, silicon-nitrides, and tetra-ethyl-ortho-silicates (TEOS). During an integrated circuit manufacturing process, these dielectrics are often etched. For example, insulating oxides are etched, protective oxides are etched, and sacrificial oxide masks are etched. Dielectrics sometimes function as insulators to isolate one level of conductors and devices from another. However, the conductors and devices on different levels must be interconnected in order to have a working integrated circuit. This is accomplished by etching holes in the dielectric layers in order to connect one layer to another. In the art of integrated circuit manufacturing, these etched holes are referred to as contacts or vias. In this document, all holes etched in a dielectric are referred to simply as contacts.
A long standing problem in the art of manufacturing integrated circuits is that of completing a process step and not knowing whether the process step completed successfully. If the step did not complete successfully, and the processing of the integrated circuit continues, then it is likely that at the end of the manufacturing process the circuit will not work as designed. Thus, continued processing after a failed process step results in wasting the costs of processing after the failed step.
In the etching of dielectrics, a problem that can cause a processing step to fail is the failure of the process to completely etch the dielectric at a contact location. This failure prevents devices from being connected. One approach to solving this problem is to design the etching process to over etch, i.e., to run the process longer than necessary for etching some contacts in order to completely etch all contacts on the substrate. One difficulty with this approach is that over etching results in some contacts being etched to dimensions larger than necessary, and this interferes with the important goal of integrated circuit manufacturing of increasing the density of the devices on a substrate.
For these and other reasons, there is a need for the present invention.
The present invention provides a system and method for overcoming the problems as described above and others that will be readily apparent to one skilled in the art from the description of the present invention below.
A system in accordance with one embodiment of the present invention for use in identifying the successful completion of a dielectric etching process on a semiconductor substrate includes a voltage probe for measuring the surface voltage of the dielectric, a selectable reference voltage, and a comparator. The selectable reference voltage is set to a value related to the surface voltage of the dielectric when the contacts are cleared of the dielectric. The comparator is coupled to the selectable reference voltage and the voltage probe. The comparator compares the measured voltage to the selectable reference voltage and produces an endpoint detection signal.
In one embodiment of the system, the voltage probe is a non-contact probe. In another embodiment of the system, the selectable reference voltage is set to a value approximately equal to the surface voltage of the dielectric when the contacts are cleared of the dielectric. In still another embodiment, the comparator is an analog comparator, and in yet another embodiment, the comparator is a digital comparator.
A method in accordance with one embodiment of the present invention for identifying the completion of a dielectric etching process on a semiconductor substrate includes the steps of setting a selectable reference voltage to a value related to the surface voltage of the dielectric when a contact is cleared of the dielectric, measuring the surface voltage of the dielectric, comparing the measured voltage to the selectable reference voltage, and identifying the successful completion of the dielectric etching process by noting when the measured voltage is less than the selectable reference voltage.
In one embodiment of a method of the present invention, the selectable reference voltage is set to a value of approximately equal to the surface voltage of the dielectric when the contacts are cleared of the dielectric. In another embodiment, measuring the surface voltage of the dielectric consists of averaging multiple measurements of the surface voltage of the dielectric.
A method for etching a dielectric on a semiconductor substrate in a plasma etch system is also described. The method includes placing a substrate with a dielectric to etch within a plasma etch chamber, setting a selectable reference voltage to a value related to the surface voltage of the dielectric when the contact is cleared of the dielectric, etching the dielectric in the plasma etch chamber, measuring the surface voltage of the dielectric, generating an endpoint detection signal when the measured voltage is less than the selectable reference voltage, detecting the endpoint detection signal, and stopping the etching when the endpoint detection signal is detected.
In one embodiment of this method, the selectable reference voltage is set to a value approximately equal to the surface dielectric voltage when the contact is cleared of the dielectric.
In another embodiment, a method for etching a dielectric on a semiconductor substrate in a plasma etch system includes placing a substrate with a dielectric to etch within a plasma etch chamber, setting a selectable reference current to a value related to the substrate current when the contact is cleared of the dielectric, etching the dielectric in the plasma etch chamber, measuring the substrate current, generating an endpoint detection signal when the measured current is greater than the selectable reference current, detecting the endpoint detection signal, and stopping the etching process when the endpoint detection signal is detected.